The present invention relates to speech generation or synthesis. The invention may be used to assist the speech of those with a disability or a medical condition such as cerebral palsy, motor neurone disease or a dysarthia following a stroke.
The invention is not limited to the above applications, but may also be used to enhance mobile or cellular communications technology, for example.
Speech generation or synthesis means the creation of speech other than through the normal interaction of brain, mouth and vocal chords. For those with a physical impairment that affects their ability to speak, the purpose of speech synthesis is to allow the person to communicate by ‘talking’ to another person.
This may be achieved by using computerised voice synthesis which is linked to a keyboard or other interface such that the user can spell out a word or sentence which will then be ‘spoken’ by the voice synthesiser.
Such systems only work where the user has already acquired literacy and has lost the ability to speak through some illness or condition after literacy has been acquired. Where the user has not acquired literacy, or loses this ability, it is necessary for the user, in effect, to learn to speak and also to acquire the basic tools of literacy related to reading and writing.
In general, when learning to read and write, two approaches may be adopted. Firstly, a learner may be invited to learn whole words, the way they sound and their meaning. Secondly, the technique known as Synthetic Phonics may be used to allow learners to break words down into their phonemes (the basic sound building blocks of words) and to sound out words.
One way that non-literate users can access words is through the use of communication boards known as lapboards or books. These boards or books are pictorial devices which allow a user to point at a picture for a second person to act as the user's voice by vocalising the sound or word associated with the picture. This system has very obvious limitations because the user is entirely reliant upon the presence and co-operation of someone else. Such circumstances discourage the user from playing or experimenting with sounds and it is known that this type of play or babble is a crucial stage in language development.
In addition there is often no logical connection between different sounds on a lapboard and it is know that certain phoneme combinations occur more readily in a specific language than others.
Computerised voice output communication devices are available which use digitized or synthetic speech to speak out letters/words/phrases. Literate users are able to spell out any number of words. However non-literate users have to use vocabulary stored by others using complex retrieval codes and sequences which impose a high cognitive load on the user. Users are also restricted to the vocabulary and cannot generate novel language as these devices are literacy based systems.